Nematoda, or roundworms, are a diverse phylum inhabiting soil, water, and as parasites in plants and animals. They have cylindrical bodies, a tough cuticle, and a complete digestive system. Nematodes play crucial roles in nutrient cycling and can impact agriculture as both pests and beneficial organisms.

Nematoda, commonly known as roundworms, have a cosmopolitan distribution and can be found in almost every environment on Earth. They inhabit regions across every continent, including North America, South America, Europe, Africa, Asia, Australia, and Antarctica.

Nematodes are highly adaptable and can thrive in a variety of environmental conditions. They inhabit diverse ecosystems, including terrestrial, freshwater, and marine environments. They are found in soil, where they play crucial roles in nutrient cycling, as well as in aquatic habitats ranging from freshwater lakes and rivers to deep oceanic sediments. Nematodes can also be found in extreme environments, such as polar regions and hot deserts, due to their ability to adapt to varying temperatures, moisture levels, and salinity.

Nematodes occupy a wide range of ecological niches. They are involved in decomposing organic matter, controlling populations of other organisms as parasites or predators, and participating in nutrient cycling. Some nematodes are free-living and feed on bacteria, fungi, or small invertebrates, while others are plant or animal parasites. Parasitic nematodes can affect agricultural crops, livestock, and even humans, making them significant in ecological, economic, and health contexts.